JPH11275860A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-loss high-efficiency DC-DC converter which is capable of lowering the voltage stress applied to a switching means. SOLUTION: One end of a first capacitor 41 is connected to one end of a second winding N2. A serial circuit of a first diode 31 and an inductor 11 is connected between the other end of the capacitor 41 and the other end of the second winding N2. The first diode 42 has a directivity such that a charging current flows to the capacitor 41 from the second winding N2, when a switch means 3 is closed. A second diode 43 makes the charging current flow into a second capacitor 44 from the second winding N2 through the first capacitor 41, when the switch means 3 is in an opened state, and constitutes a circuit which transmits the energy accumulated in the second capacitor 44 to the second capacitor 44, together with the first diode 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a DC-DC converter.

[0002]

2. Description of the Related Art In a DC-DC converter, a technique for clamping a voltage applied to a main switch means to reduce a voltage stress applied to the main switch means is disclosed, for example, in US Pat.
No. 4,441,146. In the active output circuit disclosed in this prior art document, a transformer and a main switch are inserted between both ends of a DC input terminal, and a series circuit of a clamp capacitor and an auxiliary switch is provided on the secondary side of the transformer. Are connected in parallel. By closing the auxiliary switch when the main switch is open, the voltage applied to the main switch can be clamped by the capacitor, and the voltage stress on the main switch can be reduced.

The problems of the prior art represented by the above-mentioned documents are that two switch means, a main switch means and an auxiliary switch means, are required, so that the circuit configuration becomes complicated, and the main switch means and the auxiliary switch means are required. It is necessary to prevent the switches from being closed at the same time when they are alternately closed, so that the control and drive circuits are complicated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC-DC converter capable of reducing voltage stress applied to switch means with a simple structure.

Another object of the present invention is to provide a DC-DC converter having a small loss and a high efficiency.

[0006]

In order to solve the above-mentioned problems, a DC-DC converter according to the present invention includes a transformer, a switch, and an output circuit. The main transformer has a first winding and a second winding. The switch means is connected in series to the first winding and switches a DC voltage supplied through the first winding.

[0007] The output circuit includes a first capacitor, a first diode, an inductor, a second diode, and a second capacitor. One end of the first capacitor is connected to one end of the second winding. The first diode and the inductor are connected in series, and both ends of a series circuit are connected to the other end of the first capacitor.
It is connected between the other end of the second winding.

The first diode is oriented to pass a charging current to the first capacitor through the second winding and the inductor when the switch is closed.

The second diode supplies a charging current to the second capacitor through the second winding and the first capacitor when the switching means is opened.
Further, together with the first diode, a circuit for transmitting the energy stored in the inductor to the second capacitor when the switch is closed is configured.
The second capacitor forms an output smoothing capacitor.

[0010] In the DC-DC converter according to the present invention, the switch means is connected in series to the first winding provided in the main transformer, and switches the DC voltage supplied through the first winding. The switching output is transmitted from the first winding of the main transformer to the second winding.

The second winding of the main transformer has an output circuit. The output circuit includes a first capacitor, a first diode, and an inductor. One end of the first capacitor is connected to one end of the second winding. The first diode and the inductor are connected in series, one end of the series circuit is connected to the other end of the first capacitor, and the other end is connected to the other end of the second winding. The first diode is oriented to pass a charging current to the first capacitor through the second winding and the inductor when the switch means closes. Therefore, when the switch means performs the closing operation, the first power of the main transformer is supplied from the DC power supply.
The charging current flows to the first capacitor through the second winding and the second winding. By sufficiently increasing the capacitance value of the first capacitor, the terminal voltage of the first capacitor is reduced.
It can be set to a constant value which is almost the same as the voltage value of the DC power supply converted on the secondary side.

When the switch is closed, a charging current flowing through the first capacitor passes through the inductor. For this reason, series resonance occurs between the inductor and the first capacitor, and the waveform of the flowing charging current becomes smooth. As described above, since the waveform of the current flowing through the main transformer becomes smooth, it is possible to reduce copper loss due to a skin effect generated in the core of the main transformer.

[0013] The output circuit further includes a second diode;
And a second capacitor. The second diode is connected to the first winding from the second winding when the switch means is open.
Through the second capacitor, the charging current is directed to the second capacitor. Therefore, when the switch means is in the open state, a charging current flows from the second winding of the main transformer to the second capacitor through the first capacitor. Further, the magnetic energy stored in the main lance and the electrostatic energy stored in the first capacitor during the closing period of the switch means are transmitted to the second capacitor.

Since the second capacitor forms an output smoothing capacitor, its terminal voltage can be supplied as a DC output voltage to a load connected between the DC output terminals.

When the switch is opened, the voltage generated in the second winding of the main transformer is clamped to a value obtained by subtracting the terminal voltage of the first capacitor from the DC output voltage. At both ends of the switch means, a voltage (primary-side converted clamp voltage) obtained by converting the clamp voltage (secondary-side clamp voltage) generated in the second winding to the primary side of the main transformer to the voltage value of the DC power supply. The added value occurs. The primary-side converted clamp voltage is determined by the turn ratio between the second winding and the first winding of the main transformer. Therefore, by appropriately selecting the turns ratio, the voltage applied to the switch means can be reduced, and the voltage stress can be reduced.

Moreover, the voltage applied to the switch means is substantially constant even if the input DC power supply fluctuates. As a result, it is possible to use switch means having a small withstand voltage and to use switch means having a small resistance value in the closed state.

While the charging current is flowing through the first capacitor, the inductor is excited and magnetic energy is stored in the inductor. In the present invention, the second diode included in the output circuit is a circuit for transmitting the energy accumulated in the inductor when the switch is closed to the second capacitor together with the first diode when the switch is opened. Is configured. Therefore, when the switch means is opened while the charging current is flowing through the first capacitor, the energy stored in the inductor is released through the first diode, and the charging current flows through the second capacitor. Flows. Thereby, the magnetic energy stored in the inductor is transmitted to the second capacitor, so that the magnetic energy stored in the inductor does not become a loss.

The DC-DC converter according to the present invention includes a control circuit as a general component, and the control circuit controls the switch means.

Further, the DC-DC converter according to the present invention may include, as one aspect, a second transformer and an auxiliary power supply circuit. The second transformer has two windings, and the first winding forms the inductor. The auxiliary power supply circuit generates an operation power supply for a control circuit by using a voltage generated in a second winding of the second transformer.

In the DC-DC converter according to the above aspect, one of the windings of the second transformer constitutes the above-described inductor.
A circuit loop is formed around the second winding of the transformer, the first diode, the first winding of the second transformer, and the first capacitor, and the above-described charging operation is applied to the first capacitor.

When the switch is opened, the energy stored in the first winding of the second transformer is released through the first diode and the second diode, and is supplied to the output smoothing capacitor. Charging current flows. Thereby, the magnetic energy stored in the inductor is transmitted to the second capacitor. Therefore, the magnetic energy stored in the inductor will not be lost.

When the load connected between the DC output terminals is short-circuited, the terminal voltage of the second capacitor becomes zero and the terminal voltage of the first capacitor also becomes zero. Therefore, when the switch is closed, the second
The voltage generated in the winding of
It is directly applied to the first winding of the second transformer. Therefore, a sufficient voltage is generated in the second winding of the second transformer. Therefore, a sufficient operating voltage can be supplied to the control circuit even when the load is short-circuited. This circuit operation allows the DC-DC converter to perform a constant current control operation by the control circuit, thereby supplying a stable constant current to the load.

Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings. The accompanying drawings are merely examples.

[0024]

FIG. 1 is an electric circuit diagram of a DC-DC converter according to the present invention. Referring to the figure, the DC-DC converter according to the present invention includes a main transformer 2, switch means 3, and an output circuit 4. Reference numeral 1 denotes a DC power supply, which supplies a DC voltage Vin to the DC-DC converter according to the present invention. The DC power supply 1 is a power supply or a battery that is rectified and smoothed from an AC power supply. The DC voltage Vin is supplied to input terminals T11 and T12.

The main transformer 2 includes a first winding N1 and a second winding N1.
And winding N2. The switch means 3 is connected in series to the first winding N1, and switches the DC voltage Vin supplied through the first winding N1. The switch means 3 is generally constituted by a three-terminal switch element such as an FET. The switching operation of the switch means 3 is controlled by a control signal supplied from the control circuit 6. The control of the switch means 3 is generally performed by a pulse width modulation control (PWM control) method. The control circuit 6 monitors the DC output voltage Vo appearing at the DC output terminals T21-T22, and provides the switch means 3 with voltage stabilization control so that the DC output voltage Vo becomes constant. In addition, overcurrent control and the like are also provided.

The output circuit 4 includes a first capacitor 41,
The first diode 42 and the inductor 11 are included. The first capacitor 41 has one end connected to one end of the second winding N2. The first diode 42 and the inductor 11 are connected in series, one end of the series circuit is connected to the other end of the first capacitor 41, and the other end is connected to the second winding N2.
Is connected to the other end. The first diode 42 is oriented such that a charging current flows from the second winding N2 to the first capacitor 41 when the switch means 3 is closed.

The output circuit 4 further includes a second diode 4
3 and a second capacitor 44. The second diode 43 is oriented so that a charging current flows from the second winding N2 through the first capacitor 41 to the second capacitor 44 when the switch means 3 is open. Further, the second diode 43 is connected to the switch
When the switch is opened, the energy stored in the inductor 11 when the switch 3 is closed is transmitted to the second capacitor 44 together with the first diode. The second capacitor 44 is used as an output smoothing capacitor.

Next, the operation of the DC-DC converter shown in FIG. 1 will be described with reference to FIGS. FIG. 2 is a diagram for explaining a circuit operation when the switch means 3 performs a closing operation,
FIG. 3 is a diagram for explaining a circuit operation when the switch means 3 is in an open state, and FIG. 4 shows voltage waveforms at various parts of the DC-DC converter shown in FIG. FIG. 4A shows a waveform of the voltage Vsw appearing at both ends of the switch means 3.
(B) is a voltage VD applied to both ends of the first diode 42.
4 (c) is a waveform of the voltage VD2 applied to both ends of the second diode 43, and FIG. 4 (d) is a waveform of the terminal voltage Vc of the first capacitor 41.

In the DC-DC converter shown in FIG. 1, the switch means 3 is provided in the first transformer provided in the main transformer 2.
, And switches the DC voltage Vin supplied through the first winding N1. The switching output is supplied from the first winding N1 of the main transformer 2 to the second winding N1.
To the winding N2.

An output circuit 4 is provided on the second winding N2 of the main transformer 2. The output circuit 4 includes a first capacitor 41 and a first diode 42. The first capacitor 41 has one end connected to one end of the second winding N2. The first diode 42 and the inductor 11 are connected in series to form a series circuit, one end of the series circuit is connected to the other end of the first capacitor 41, and the other end of the series circuit is connected to the second winding N2. Is connected to the other end.

Therefore, when the switch means 3 performs the closing operation (see FIG. 2), the second winding N2 of the main transformer 2, the first
A circuit loop surrounding the capacitor 41, the first diode 42, and the inductor 11 is formed.

Further, the first diode 42 is oriented so that the charging current Ic flows from the second winding N2 to the first capacitor 41 when the switch means 3 is performing the closing operation. Therefore, during the period from t0 to t1 (see FIG. 4) when the switch means 3 is performing the closing operation, the DC power
From the first winding N1 and the second winding N of the main transformer 2
2 and further through the inductor 11 and the first diode 42 to the first capacitor 41
(See FIG. 2) flows. By sufficiently increasing the capacitance value of the first capacitor 41, the first capacitor 41
Becomes substantially constant (see FIG. 4D), and becomes the voltage value of the DC power supply 1 converted to the secondary side.

T0 when the switch means 3 is performing the closing operation
At t1, the charging current Ic (see FIG. 2) flows from the DC power supply 1 to the first capacitor 41 through the first winding N1 and the second winding N2 of the main transformer 2, thereby causing the first Electrostatic energy is stored in the capacitor 41 and magnetic energy is stored in the core of the main transformer 2.

The second diode 43 of the output circuit 4 is connected to the second diode of the main transformer 2 when the switch means 3 is opened.
Through the first capacitor 41 from the winding N2 to the second capacitor 44. Accordingly, during the period from t1 to t2 (see FIG. 4) when the switch means 3 is in the open state (see FIG. 3),
A charging current IF flows from the second winding N2 of the main transformer 2 through the first capacitor 41 and further through the second diode 43 to the second capacitor 44. As a result, the magnetic energy stored in the main transformer 2 and the electrostatic energy stored in the first capacitor 41 during the closing period of the switch means 3 are transmitted to the second capacitor 44. The opening period of the switch means 3 is from t1 to t3, but energy transmission is not performed from t2 to t3.

Since the second capacitor 44 constitutes an output smoothing capacitor and is connected between the DC output terminals T21 and T22, the terminal voltage of the second capacitor 44 is set as the DC output voltage Vo and the DC output terminal It is supplied to the load 5 connected between T21 and T22.

When the switch means 3 is opened, the voltage VF (see FIG. 3) generated in the second winding N2 of the main transformer 2 is changed from the DC output voltage Vo to the first capacitor 41.
Is clamped to a value obtained by subtracting the terminal voltage Vc of At both ends of the switch means 3, a DC voltage Vin supplied from the DC power supply 1 and a voltage obtained by converting a clamp voltage (secondary clamp voltage) generated in the second winding N2 to a primary side (primary side converted clamp). A voltage Vsw is generated by adding the voltage Vnp.
The primary-side converted clamp voltage Vnp is equal to the second
Of the winding N2 and the first winding N1. This relationship is expressed by an equation: Vc = (Ns / Np) Vin (1) Vnp = (Np / Ns) (Vo−Vc) (2) Vsw = Vin + Vnp (3) Equations (1), (2) and From (3), Vsw = (Np / Ns) Vo, where Vo: DC output voltage Np: number of turns of the first winding N1 of the main transformer 2 Ns: number of turns of the second winding N2 of the main transformer 2

As is apparent from the above equation, the turns ratio (Np
/ Ns), the switching means 3
Can be reduced, and the voltage stress can be reduced. Further, by reducing the voltage stress applied to the switch means 3, the switch means 3 having a smaller resistance value during conduction can be used as compared with the conventional one, and the loss occurring during the conduction period of the switch means 3 can be reduced as compared with the conventional one. be able to.

When the switch 3 is closed, the charging current Ic flowing through the first capacitor 41 passes through the inductor 11, so that a series resonance occurs between the inductor 11 and the first capacitor 41 and flows. Charging current I
c becomes a sine waveform. Therefore, the waveform of the current flowing through the switch means 3 is a waveform in which the sawtooth exciting current flowing through the main transformer 2 and the resonance current flowing into the first capacitor 41 are superimposed. For this reason, the high frequency component of the current waveform flowing through the main transformer 2 is reduced, so that copper loss due to the skin effect of the high frequency component can be reduced. Further, generation of noise can be reduced.

As described above, the charging current Ic flowing through the first capacitor 41 (see FIG. 2) passes through the inductor 11. Therefore, while the charging current Ic is flowing through the first capacitor 41, the inductor 11 is excited,
Magnetic energy is stored in the inductor 11.

When the switch means 3 is opened while the charging current Ic is flowing through the first capacitor 41,
The charging current I from the inductor 11 to the second capacitor 44
L (see FIG. 3), thereby causing the inductor 11
The magnetic energy stored in the second capacitor 44
Is transmitted to Therefore, there is no possibility that the magnetic energy stored in the inductor 11 will be lost.

FIG. 5 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention. 5, the same components as those in FIGS. 1, 2, and 3 are denoted by the same reference numerals, and description thereof will be omitted. DC shown in FIG.
The DC converter includes a second transformer 7 and an auxiliary power supply circuit 8.

The main transformer 2 has a third winding N3, and the third winding N3 of the main transformer 2 is
It is connected to the. An output current detection circuit 9 is connected to the load 5 in series.

The control circuit 6 is supplied with the operating voltage from the auxiliary power supply circuit 8 and gives the switch means 3 voltage stabilization control so that the DC output voltage Vo is constant. Control circuit 6
Monitors the DC output current Io based on the current detection signal supplied from the output current detection circuit 9, and provides the constant current control to the switch means 3.

Next, the second transformer 7 is connected to the first winding 1.
1 and a second winding 12. The first winding 11 is
This constitutes the inductor 11 (see FIGS. 1 to 4). The operation and effect of the first winding 11 are the same as those of the inductor 1 shown in FIGS.
Since it is exactly the same as 1, the description is omitted. The second winding 12 provided in the second transformer 7 includes an auxiliary power supply circuit 8
It is connected to the. Therefore, the auxiliary power supply circuit 8 receives supply of energy from both the third winding N3 of the main transformer 2 and the second winding 12 of the second transformer 7.

When operating with the normal load 5, the DC-DC converter operates at a constant voltage and the third
A sufficient voltage is generated in the winding N3. Third winding N3
Is used for the auxiliary power supply circuit 8. The control circuit 6 operates stably by the operating voltage supplied from the third winding N3 and the auxiliary power supply circuit 8.

Next, when a load short circuit occurs, DC-DC
The converter operates as a constant current source. In this case, the conduction period of the switch means 3 is controlled to be very short by the control circuit 6. For this reason, when the circuit constituted by the third winding N3 and the auxiliary power supply circuit 8 is of a forward type, the voltage generated in the third winding N3 is equal to the voltage of the first winding N3.
Does not become a value determined by the turn ratio between the third winding N1 and the third winding N3, but decreases. When the circuit constituted by the third winding N3 and the auxiliary power supply circuit 8 is of a flyback type, the voltage generated in the third winding N3 becomes zero.

On the other hand, the second transformer 7 includes the first winding 1
1 has a second winding 12 coupled thereto, and energy is supplied from the second winding 12 to the auxiliary power supply circuit 8. When a load short circuit occurs, the second capacitor 44
And the terminal voltage of the first capacitor 41 becomes zero. Then, when the switch means 3 is closed, the voltage generated in the second winding N2 of the main transformer 2 is applied to the first winding 11 of the transformer 7 and the voltage is applied to the second winding 12. Occur. This voltage is supplied to the auxiliary power supply circuit 8. For this reason, even when a load short circuit occurs, sufficient energy is supplied to the auxiliary power supply circuit 8 to cause the DC-DC converter to perform a constant current control operation by the control circuit 6 so that the load 5 becomes stable. A constant current can be supplied.

Conventionally, a circuit for obtaining an operating power supply of the control circuit 6 from a voltage drop of the output current detection circuit 9 has been known.
However, in this case, it is necessary to increase the impedance of the output current detection circuit 9, and inevitably causes a large loss in the output current detection circuit 9. On the other hand, in the case of the embodiment shown in FIG. 5, since the operating power supply of the control circuit 6 is obtained by using the voltage generated in the second transformer 7, the impedance of the output current detection circuit 9 must be reduced. And loss can be reduced.

FIG. 6 is a specific electric circuit diagram of the auxiliary power supply circuit 8 in the DC-DC converter shown in FIG. In FIG. 6, the same components as those in FIG.
The same reference numerals are given and the description is omitted.

The auxiliary power supply circuit 8 includes a third diode 81
, A fourth diode 82, and a third capacitor 83. The third diode 81 is connected to the main transformer 2
Is connected in series with the third winding N3 to form a series circuit, and both ends of the series circuit are connected to both ends of the third capacitor 83. Third capacitor 83 forms a smoothing capacitor in auxiliary power supply circuit 8.

The third diode 81 is connected to the switch means 3
In the open state, the third winding N3 of the main transformer 2
Of the capacitor 83 (a flyback method). However, the third diode 81 is connected to the main transformer 2 when the switch means 3 is closed.
Of the third winding N3 to the third capacitor 83.

The fourth diode 82 is connected in series to the second winding 12 of the second transformer 7 to form a series circuit, and both ends of the series circuit are connected to both ends of the third capacitor 83. ing. The fourth diode 82 is connected to the second winding 12 of the second transformer 7 when the switch 3 closes.
From the first capacitor 83 to the third capacitor 83.

As described above, in the illustrated auxiliary power supply circuit 8, both ends of a series circuit formed by connecting the third diode 81 and the third winding N3 of the main transformer 2 in series It is connected to both ends of the third capacitor 83. Accordingly, a charging loop is formed around the third winding N3 of the main transformer 2, the third diode 81, and the third capacitor 83. In the embodiment, the third diode 8
1 is oriented so that a charging current flows from the third winding N3 of the main transformer 2 to the third capacitor 83 when the switch means 3 is in the open state. A charging current flows from the third winding N3 of the transformer 2 to the third capacitor 83 through the third diode 81, and the third capacitor 83 is charged to the terminal voltage V02. This terminal voltage V02 is supplied to the control circuit 6.

The fourth diode 82 is connected in series to the second winding 12 provided in the second transformer 7 to form a series circuit. Both ends of this series circuit are connected to both ends of the third capacitor 83. Therefore, the second winding 12 of the second transformer 7, the fourth diode 82 and the third
A charging circuit loop surrounding the capacitor 83 is formed.

The fourth diode 82 is connected to the switch 3
During the closing operation, the charging current is directed from the second winding 12 of the second transformer 7 to the third capacitor 83. Therefore, when the switch means 3 is closed, the fourth winding 12 provided in the second transformer 7
, A charging current flows to the third capacitor 83, and the third capacitor 83 is connected to the terminal voltage V02.
Charged up to. This terminal voltage V02 is supplied to the control circuit 6.

Next, the operation of the DC-DC converter shown in FIG. 6 will be described. First, in the steady operation region, the third capacitor 83 is charged through the third diode 81 by the voltage Vh generated in the third winding N3 of the main transformer 2.

When the load 5 is short-circuited, the third winding N
Although the voltage Vh generated at 3 is zero, the voltage Vg is generated at the second winding 12 provided in the second transformer 7.
The third capacitor 83 is charged by the voltage Vg of the second winding 12 through the fourth diode 82.

When the load 5 is short-circuited, the terminal voltages of the second capacitor 44 and the first capacitor 41 become zero, and the second winding N2 of the main transformer 2 is closed while the switch means 3 is closed. Is applied to the first winding 11 provided in the second transformer 7. At the same time, the second
A voltage Vg is generated in the second winding 12 provided in the transformer 7, and a charging current flows into the third capacitor 83.
Thus, even when the load is short-circuited, the third capacitor 83
Does not decrease, and the control circuit 6 operates stably. Therefore, DC-D
The constant current operation can be reliably performed by the C converter.

When the load is short-circuited, the voltage Vg generated in the second winding 12 of the second transformer 7 and the voltage Vg generated in the third winding N3 of the first main transformer 2 are: Vh> Vg
So that the first winding 11 of the second transformer 7 is
And the ratio of the number of turns to the second winding 12 is determined.

FIG. 7 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention. 7, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the third winding N3 of the main transformer 2 and the second winding 1 of the second transformer 7
2 are connected in series with the same polarity. A third diode 81 is connected in series with the series circuit of the third winding N3 and the second winding 12. Third diode 8
The polarity of the first winding 12 depends on the voltage Vh generated in the third winding N3 and the second winding 12 when the switch means 3 performs the closing operation.
Is selected so as to be in the forward direction (forward system) with respect to the voltage Vg generated at the time.

In the normal operation region, the capacitor 83 is charged through the third diode 81 by the voltage generated in the third winding N3 of the main transformer 2.

When the load 5 is short-circuited, the third winding N
Although the voltage Vh generated at 3 decreases for the above-mentioned reason, the voltage Vg is generated at the second winding 12 provided in the second transformer 7. The third capacitor 83 is charged through the third diode 81 by the sum (Vh + Vg) of the reduced voltage Vh and the voltage Vg generated in the second winding 12. As a result, even when the load is short-circuited, the third
The terminal voltage V02 of the capacitor 83 does not decrease, and the control circuit 6 operates stably. Therefore, when the load is short-circuited, the DC-DC converter can reliably perform the constant current operation.

FIG. 8 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention. 8, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a circuit portion of the auxiliary power supply circuit 8 that uses the voltage Vh generated in the third winding N3 of the main transformer 2 is a fourth capacitor 84.
And a fifth diode 85. One end of the fourth capacitor 84 is connected to one end of the third winding N3 of the main transformer 2. The fifth diode 85 is oriented so that a charging current flows from the third winding N3 to the fourth capacitor 84 when the switch means 3 is closed.

The auxiliary power supply circuit 4 further includes a sixth diode 86. The sixth diode 86 is oriented such that a charging current flows from the third winding N3 to the third capacitor 83 through the fourth capacitor 84 when the switch means 3 is in the open state.

The circuit configuration of the above-described auxiliary power supply circuit 8 includes the second winding N2 of the main transformer 2, the first capacitor 41,
The first diode 42, the second diode 42, and the second
This is basically the same as the circuit configuration using the capacitor 44, and has the same effect. Therefore, during normal operation,
Even when the input voltage changes, the terminal voltage V02 of the third capacitor 83 supplied to the control circuit 6 can be kept constant. For this reason, the loss generated in the auxiliary power supply circuit 8 can be made constant, and the value of the voltage V02 can be set lower than in the conventional case, and the loss generated in the auxiliary power supply circuit 8 can be reduced.

When the load 5 is short-circuited, the third winding N
Although the voltage Vh generated in the third transformer 7 decreases, the second transformer 7
, A voltage Vg is generated in the second winding 12 provided in the first stage. The third capacitor 83 is charged by the voltage Vg through the third diode 82. Thus, even when the load is short-circuited, the terminal voltage V02 of the third capacitor 83 does not decrease, and the control circuit 6 operates stably. Therefore, when the load is short-circuited, the DC-DC converter can reliably perform the constant current operation.

[0067]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a DC-DC converter capable of reducing the voltage stress applied to the switch means with a simple configuration. (B) A DC-DC converter with small loss and high efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a DC-DC converter according to the present invention.

FIG. 2 is a diagram illustrating a circuit operation when a switch unit performs a closing operation in the DC-DC converter illustrated in FIG. 1;

FIG. 3 shows a DC-DC converter shown in FIG.
FIG. 5 is a diagram illustrating a circuit operation when the switch unit is in an open state.

FIG. 4 shows voltage waveforms at various parts of the DC-DC converter shown in FIG.

FIG. 5 is an electric circuit diagram showing another embodiment of the DC-DC converter according to the present invention.

FIG. 6 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention.

FIG. 7 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention.

FIG. 8 is an electric circuit diagram showing still another embodiment of the DC-DC converter according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Main transformer 3 Switching means 4 Output circuit 41 First capacitor 42 First diode 11 Inductor 43 Second diode 44 Second capacitor 5 Load

Claims (8)

[Claims] 1. A DC-DC converter including a main transformer, switch means, and an output circuit, wherein the main transformer has a first winding and a second winding, The switch means is connected in series to the first winding and switches a DC voltage supplied through the first winding. The output circuit includes a first capacitor, a first diode, An inductor, a second diode, and a second capacitor, wherein the first capacitor has one end connected to one end of the second winding, and the first diode and the inductor Are connected in series, both ends of a series circuit are connected between the other end of the capacitor and the other end of the second winding, and the first diode is configured to close the switch means. Sometimes the second winding and the front The second diode is directed to pass a charging current to the capacitor through the inductor, and wherein the second diode passes through the second winding and the capacitor when the switch means is opened. A circuit for transmitting a charging current to the second capacitor and transmitting the energy stored in the inductor to the second capacitor together with the first diode at the time of closing the switch means; Is an output smoothing capacitor D
C-DC converter. 2. The DC-DC converter according to claim 1, further comprising a control circuit, wherein said control circuit controls said switch means. 3. The DC-DC converter according to claim 2, further comprising a second transformer and an auxiliary power circuit, wherein the second transformer has a first winding, A second winding, wherein the first winding of the second transformer constitutes the inductor, and the auxiliary power supply circuit comprises a second winding of the second transformer. A DC-DC converter that generates an operation power supply for the control circuit by using a voltage generated in the control circuit. 4. The DC-DC converter according to claim 3, wherein the main transformer further has a third winding, and the auxiliary power supply circuit has a third winding. DC-DC converter using the voltage generated in the DC-DC converter. 5. The DC-DC converter according to claim 4, wherein the second transformer has a voltage lower than a voltage generated in the third winding of the main transformer when a load is short-circuited. The DC-turn ratio of the two windings is selected so that a large voltage is generated in the other of the two windings.
DC converter. 6. The DC-DC converter according to claim 4, further comprising a third diode, wherein said third winding of said main transformer and a second winding of said second transformer are provided. And the third diode is connected in series with the same polarity. The third diode is connected to a series circuit of the third winding of the main transformer and the second winding of the second transformer. Are connected in series, and when the switch means performs a closing operation, a forward voltage is applied to a voltage generated in the third winding of the main transformer and a voltage generated in the second winding of the second transformer. DC-DC converter that is selected to be. 7. The DC-DC converter according to claim 4, wherein the auxiliary power supply circuit includes a fourth capacitor, a fifth diode, and a sixth diode. One end of the capacitor is connected to one end of the third winding of the main transformer, and the fifth diode is connected to the fourth winding from the third winding when the switch is closed. The sixth diode is oriented to discharge the charge stored in the fourth capacitor when the switch means is open. DC-DC converter. 8. The DC-DC converter according to claim 2, further comprising: an output current detection circuit, wherein the control circuit comprises: A DC-DC converter that controls the switch means based on an output current detection signal supplied from an output current detection circuit.